Electron beam tube



July 12, 1960 KERN K. N. CHANG ELECTRON BEAM TUBE Filed Aug. 31, 1956 M MW , .Second WW *nn4 ,4 A,

13 9 5 ELEcrRoN EBEAM panamawe e a? Filed Aug. 31, 1956 ;S er."No. 607,362 I totalses inventiorilrelates to electron beam tubes and in pa ularjto improved focusing meansfor such tubes. wh le not limited theii'eto, the. invention. isiherein described embodiedin a traveling wave tube.

Inbeam tubes it'is pften desirable.tomatch two different foeusing fields of the tube to each other so as to pro- K. Cha g, Briueeton, N h, assignor to'iRa di o .vidda snioothtransition region between the two fields for -the electron beam lof the tube, the smooth transition region being desirable inorderto minimize oscillation of .eflectrens in theira-paths and to' thus maintain an elec- 1 l: bea I;.$ l?. fii .1Y mi l F e'xamPle, 3:11 is often desirable to -pgovide, r0; a traveling wave tube, an electron gun immersed in a constant magnetic focusing field suchas a field'produced by a solenoid, and to immc sefli d la li n-Q t e e inc P i i magnetic focusing field spaced from the electron gun fieldfor main- Patented July 121,

tube 1.0 in which the invention may be used. Within elongated envelope 12, and at one end thereof, is an electron gun' 14 which may include a cathode 16 having ;ajheater (not;show n) and a plurality of accelerating electrodes l fi, 20, 22, and 24 for: collimating electrons,

emitted from the cathode 16, to produce a beam of elec trons with parallel fiow. along theaxis of the envelope 12.

The beam tube shown byway of example includes adelay'line structure in the form of a helix 28 which ex- ..tends axially of the envelope 1;. An electron collecting element or collector electrode 30 is positioned within the envelope 12 at the end thereof remote from the electron gun-14. The collector electrode 30 and the electrongun 14 define between them the path of travel of the elwtron beam. In operation, a direct current power supply. (not shown), would be connected to the electron gun elements 14, the helix 28,- and the collector electrode 30, in order to maintain them at the desired direct current potentials with respect to each other. 7

A solenoid 34 around the electron gun 14 provides a constant axial magnetic focusing field along afirst region of the tube'including the cathode 16 and a portion of the path of the electron beam adjacent to thecathode to along' a second region of the electron beam path spaced .tainingthe beamfocused in its path of travel adjacent:

,passage from one field to the other.

lt is another object of the invention to provide an improved-traveling wave tube having a substantially laminar {flow of; electrons through two spaced magnetic focusing .-fie lds.of diiferent kinds and wherein the electrons in the beam. are maintained substantially laminar 'fiow through,-the pas sage thereof between the twofields.

flhipjoregoing and relatedobjects are realized in an electron: beam tube comprising electron gun including a cathode for projecting an electron beam along a given (path, means for producing a constant magnetic, electron beam focusing field that is, a'unidire'ctional magnetic fieldof a given constant strength, alonga first region of :the path including-the cathode for maintaining the beam 't f p eafalongthefirst region, means for producingfa ;pei 'iodic,m agneticelectron beam focusing field along a region of the electron beam path spacedffrom the (a region of the path a peak focusing field strength greater than uid'sfrengrh of the first field, and

za focusing lens vofadjiastalzyle fieldstrength adjacent to jmacm fends ofthe two i'regionsfor providing a transition magnetic beam focusing field between the adjacent ends of the'two regions.

i Tth e-drawingwherelike numerals refer to like parts: 1 is a longitudinal sectional view of a beam tube of the travelinglwave type erribodying the invention; and

:1 2 d 3.are diagranis'fillustrating the operation ;of;the tube,ofFig.1I-

Bre g now to lthe drawing in greater detail, there shown in Fig. l onefo'mi of traveling wave amplifier "maintain-parallel 'electronflo-w in the firstregion, as indicated by the'linear beam path shown in Fig.1 1'. A periodic magnetic beam focusing structure 36 is positioned aro'und thetube envelope 12 along a portion of the tube remote from the electron gun 14 and axially spaced from thesolenoid 34. This periodic structure 36 produces a periodic second magnetic beam focusing field fromltheaforementioned first region formaintaihing the lelectron hear'n' focused for parallel electron flow along its path'oftravel adjacent. to the helix 28. Preferably, the root mean square of the strength of the periodic field issubs'tantially equal to the strength of the constant field so as ,to subject the electron'beam in the second region (the region adjacent to the periodic structure) to a focusing field of the same average strength as that of the field.

in the first region (the region; adjacent to the solenoid '34). The periodic magnetic structure 36 is comprised qffanumber of axially-spaced, axially-polarized, ring jmagnets'3 8. The magnets 38 are arranged with like poles adjacent to eachother so as to produce, along the path of travel of the beam in the region of the helix,

an alternating series of oppositelydirected magnetic focusing fields. Ring-shaped pole pieces 48 are disposed between adjacent magnets 38 to better direct the magnetic flux ofthe magnets along thebeam path adjacent to the helix '28, The magnets 38 are supported in the desired relation adjacent to the helix by means of a support frame 42. i' lfhe input and output connectionsto'thelhelix 28 are made bywaveguid'es 44and46, respectively. The supportframe 42 and'ithe Waveguides 44 and 46 are of arty magnetically transparent metal such as copper. The

portion of the periodic magnetic structure 36 adjacent-to the input waveguide 44 takes the form of a ring magnet 38a having an inner diameter sufficient to extend around the portion of the Waveguide'44 adjacent to the envelope 12 so that electromagnetic energy transfer'between the 'wavcguide'and are helix may be effectedwithout any substantial disturbance of the magnetic field of the periodic structure 36. The larger diameter magnet 38a has a larger cross section than that of the other magnets 30 and consequently has a stronger magnetic field which compensates for its greater distance from the helix.

According to the invention there is provided, along a region of the beam path between the constant magnetic field of the-solenoidf34 and the periodic magnetic field of the magnet structure 36, a magnetic'lens of adjustable field" strength for providing a transition beam focusing field between the constant and periodic fields aforementioned. In the form of the invention illustrated 'in Fig: l; the magnetic lens of adjustable field-strength-takes the form of a second solenoid 50 disposed between the first solenoid 34 and the periodic magnetic structure 36. The/second solenoid 501s provided withtwo'ri-ng shaped pole pieces 52 and 54f-on the sides of thesecondsol'enoid 50 adjacentto, respectively, the first solenoid 34 and the periodicstructure; 36'. 'This adjustable magnetic; lens;(the

second solenoid .50 being adjustable by virtue of the fact that the field strength of the second-solenoidis adjustable by varying the amount of electric current therethrough) between the adjacent ends of the first and second-regions,

produces an adjustable transition beam focusing field that is, between the constantmagnetic field in the elec- 't'rorr gun region of the tube and; the-periodic magnetic fieldin thejh elix region of the tube, for maintaining the electrons inthe beam in; a smooth parallel flowduring theirpassage between the time-constant and: periodic fields. Y

' Referring now to Fig. 2, there is illustrated the; configuration of t-hemagnetic fields along the electron beam path of the tube of Fig. 1. B represents the magnetic field strength of the constant field in the region of the electron gun, B represents the peak magnetic field strength of the periodic magnetic strncture in the region of the electron beam along the helix,- B being equal to V 28 The dot-dash line 60 represents the magnetic field strength; in the region along the beam path (Fig. 1.) between solenoid 54 and the periodic structure 36.

.' The field configuration oi the transition field lens along the tube axis is accordingto the following. Let the value of'the axial magnetic field B (Fig. 2) at the two axial ends of the transition field 60 befixed at B4, and B re- B t-WET), is representedbyline 62: According to Equation 1 the area A of the square of the field below the dashed line 64 of B equals the area of the square of the field A above the line of B This gives a graphic solution to the design of the field strength required of the transition lens 50. 1 1

From the foregoing iris seen that an improved electron beam tube isiprovid'edi includinggtyvtog'spaced magnetic lect n sautfa ins e ds. Q ..di e ntk d lpneth pat gt ve i i agree he ubal east. tr? .sit magnetic field means between the magnetic fields of such character that the. electrons; the. are, maintained in a substantially smooth flow during their passage from one field to the other."

a constant firstmagn'eticfocusing'field; of 'a given strength along a first region ofsaid path including said: cathode, means foir Pr u i a P r dic. gnet s a n e focusingfiel'd along a second region on said path spaced from saidfirstregion and having a pealr 'strength at the .spectively (the axial endsjbeing O, and' Then sub-' stantially any transition field. configuration will provide the smooth transition according'to the inventionfit filig. 3) the integral (area A of the square of the amount of the magnetic field (that is, if the integral of the amount of the magnetic force, since the square of the magnetic field is proportional. to the magnetic force) less than the square of the magnetic field at z=0 (thatis B is equal to the integral (area A of the amount of the magnetic field greater than B In other words, with the field strengths of the ends of the transition field fixed at B and [ZB' at axial points 0 and L, respectively, asmooth transition between the fields at opposite axial ends oi the transition field is provided when area A equals area A that is, when tube axis. Whenthe root mean square of the periodic end of said second region" neares-tjto said-first regionsub- .stantially greater than said given strength of said first magnetic field, andmagnetic field producing means, separate fromtsaid first andsecondnamed means, forproducing a transition magnetic beam focusing field along a third region extending betweenthe adjacent ends of said spacedf regions. l i p 22' An electron beam tube accordin g to claim 1; wherein said meansv for producing said magneticfieldxnom 'prisesa solenoid-Q n V 3. An electron beam tube according to claiin;1 wherein the magnetic field strength of saidfirst magnetic field is substantially equal to the {roof mean' square of the peak value of' the field strength of" said: periodic second magnetic field. Y

4. A traveling wave tube comprising means including a cathode for projecting a parallel flow electron beam along a given path; an elongated signal w ave propagating structure disposed adjacent to said path and adapted to propagate a traveling signal wave along said structure, means for producing a'coristant ma'gnet-icbeam tocnsing field of a given stfength along a first region of saidpath including said cathode formaintainingsaid beam field is equal to the constant field, in the example of Fig.

1, the smooth transition is a substantially laminarfiow tire path of travel of the electrons.

For convenience, the axial extent L of the transition '55 ofelectroris'ifi the beam throughout substantially the enfield. is chosen to be equal to the axial extent of one period. of the periodic magnetic structure 36. However, a lesser or greater transition field axial extent may instead be used provided that the axial length L, of the transition field is relatively small, that is, less than about I one-fourth of the scalloping-wave-length of the beam in the constant field B For the derivation of Equation 1, reference is herebyrnade to my paper entitled Periodic Magnetic Field Focusing for Low-Noise Traveling-Wave Tubes, published .in RCA Review, September 1955. Equation 1 herein is the same as Equation 51 4 in said paper.

Using Equation 1., f simple to design graphic transition field by plotting B versus z and choosing a field distributionaccording to Equation 1.. Thisis shown in Fig. 3. Supposethe square of the field, strength of a match n sp suqid. 51Lv whi h. mama 1 112 see aw .ttsld ally any.

focusing field.

a a'pre'det ermined transverse extent along said firstregion, means for producinga periodic magnetic beam focusing field along a; second region of said path speed from said first region and including said; structure" having a peak magnetic field strength at end-of said second region nearest to said region substantiallygreater than said given strength of said'firstmagneticlfield, and a soleiioid otfadjustable fieldstrength efliectjve'in a region extending between said" spaced first and s co a ons for me i ne a tr n-s ti electron m o s n a t fie thetebstws n f Y 5 A. r v ng'WeYQtu @QQQ i 1 2Q 4 h in a d means o p oduci sa d. 9i sll a ae, a fi t re on omp ises g e a ds a wher n t s: s c fie t n Qt ahbwhfsus 3;??115 (E151 rs e i ubs t al y equal to the r btmeaat u r ofthe peak value ofthelfieldistrengjth said penio c n ec o br am bg Q Ii$i 8-n inc udi a cathode o p qie i lec on. s mj l la a x n path; means for producing a constantgfirst'mag netigbeam focusing field of a. given strength B alnnga first region f d'i including sa d a hgd fa 'm i t s 'said a he: a tist sa d sq ml r g n rare to 7 said first region substantially equal to /2 times the field where dz is the increment of the distance along said beam path, and B is the strength of said transition field at any given point along said beam path between said adjacent ends of said first and second regions.

7. An electron beam tube according to claim 3, wherewhere L is the distance between said first and second regions, dz is the increment of the distance 2 along the beam path between z=0 and z=L, B is the strength of the transition magnetic field at any distance 2 and B is the given strength of the first magnetic field.

References Cited in the file of this patent UNITED STATES PATENTS 2,306,875 Fremlin Dec. 29, 1942 2,602,148 Pierce July 1, 1952 2,632,130 Hull Mar. 17, 1953 2,741,718 Wang Apr. 10, 1956 2,781,472 Clavier Feb. 12, 1957 2,801,361 Pierce July 30, 1957 2,804,548 Ruska Aug. 27, 1957 2,828,434 Klein et a1. Mar. 25, 1958 2,841,739 Pierce July 1, 1958 2,844,750 Veith et al. July 22, 1958 2,844,754 Ciofl'i July 22, 1958 2,847,607 Pierce Aug. 12, 1953 FOREIGN PATENTS 153,551 Australia Oct. 8, 1953 1,080,230 France May 26, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 2 945, 153 July 12 1960 Kern K N, Chang It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 33,- before "is" insert, field line 39 after "focusing" insert fielda -=-=g column 3 lines 27 and 45, for 28 each occurrence read [5 B column 4 line 2 for ""B (2-\/B read w B (Z /R a Signed and sealed this 20th day of November 1962,

(SEAL) Attest:

ERNEST w. SWIDER DAVID D Attesting Officer Commissioner of Patents 

